Traffic actuated control system and apparatus



Dec. 19, 1939. w cox 2,183,780

TRAFFIC ACTUATED CONTROL SYSTEM AND APPARATUS Filed April 15, 1936 5Sheets-Sheet 1 '1 l 7 F- INVENTOR HAPPY A. W/zcaa A TTOR N E Y5 H. A.WlLCOX Dec. 19, 1939.

TRAFFIC ACTUATED CONTROL SYSTEM AND APPARATUS Filed April 15, 1936 5Sheets-Sheet 3 A TTORNEYJ H. A. WILCOX Dec. 19, 1939.

TRAFFIC ACTUATED CONTROL SYSTEM 'AND APPARATUS 5 SheetsShee 4 FiledApril 15, 1956 WM NMN 3 3 ATTORNEYS 5 SheetsSheet 5 Dec. 19, 1939. H. A.WILCOX TRAFFIC ACTUATED CONTROL SYSTEM AND APPARATUS Filed April 15,1936 Patented Dec. 19,1939] um rso STAT Harry A. Wilcox, Bronxvllle, N.Y., asaignor to Automatic Signal Corporation, New York, N. Y.,

a corporation of Delaware Application April 15, 1936, Serial No. 74,422

23 Claims.

This invention relates to a trafllc system capable of use at theintersection of two tramc lanes or streets, and has for its generalobject to provide an automatic system by means of which traflic will beexpeditiously and safely handled. This system is to a large extentcontrolled by the traffic along the intersecting lanes. Its operationwill be responsive not only to the presence of traffic but will beaffected also by the density of trailic in each lane. Previous systemsto my knowledge have provided for traflic actuation of the signals buthave less completely taken into account the element of the relativedensity of trafflc in the two lanes when traffic is very heavy.

The vehicle actuated traffic control is notin itself ainew invention,such systems having been in general use for some time. Previous systemshave served admirably to control traflic at the intersection of twolanes when tramc is light in one lane and heavy in the other, or whentraflic is irregularly spaced in one or both of said lanes, but theyhave not been adapted so well to the most efllcient handling ofintersections where traflic is continuously heavy in both lanes. systemto be effective under this latter condition must be sensitive to slightdifference between two heavy traflicv flows.

The system disclosed herein handles efllcient'ly any type of traffic'but is especially effective in handling heavy traflic with the utmostefliciency. This system is of the type in which within a maximum limiteach vehicle approaching. the intersection on a go signal after aninitial interval which is preferably inserted as'described for a timeafter its approach, such time being designated as a vehicle protectionperiod, right' ES PATENT orrica denser trafiic thereby providing formaximum efficiency in handling heavily travelledintersections whereefliciency is of the greatest importance. In effect it provides meanswhereby waiting traflic is able to exert a forcing eifect to obtain 6 Ithe right of way sooner in accordance with its demand.

This system, like previous vehicle actuated I trafl'lc control systems,includes stop, and "go signals to be displayed in each traflic' laneenterl0 ing an intersection, a control mechanism to operate the stop andgo signals, and trailic detectors located in the aforementioned trafficlanes, which effect the operation of the control mechanism in such amanner as to cause the signal 15' display periods to conform to therequirements of the trafiic approaching the intersection. In this systemas in the prior types of vehicle actuated systems the actuation of atraflic detector in a traiilc lane in which. the stop signal is beingdis-. 20

I played causes the right of way to be transferred below extends theperiod of display of such signal interval in this new system isdecreased in-ac- .cordance with the number of. vehicles awaiting" on thecross lane. Hence, with a large group of vehicles waitingon the crosslane, each vehicle entering the intersection from the lane in which thego signal is being displayed is allotted a shortened time period for itspassage. As a result .of this fact a shorter spacing-between vehicles inthe moving line will yield the right of way. Therefore under the systemdisclosed 50' herein a large number of waiting vehicles is moreeffective than a small number to cause transfer of the right of way tothe lane in which they are waiting. This invention therefore provides asystem in which the right of way tends 55- to revert more quickly to thelane having the to that lane at the .flrstsopportunity. If there is notrailic entering the intersection from the lane in which the goflsignalis being displayed a caution signal is usually immediately displayed insaid lane and after a short period the right of way is transferred tothe lane in which the stop signal was being displayed.

If traflic is moving in the lane wherein the .go signal is beingdisplayed the actuation of 30 the traflic'detector in the lane in whichthe stop signal is beingdisplayed causes the right of way to betransferred thereto at the first break of a predetermined time in thesaid moving traffic. If no such break occurs in said movin traffic theright of way will be transferred at the end of a predetermined maximumperiod usually provided by a different timing element.

' In this system as in previous systems, the actuation of a trafllcdetector during the period in which the go signal is being displayed tothe lane wherein said traffic detector is located causes such go signalperiod to be extended under certain conditions. The go period for eachtraflic lane is divided into two parts. Dur- 5 ing the first part ofthis period the actuation of the traflic detector in the lane in whichthe go signal is being displayed is of no effect. This first part of thego period, called the initial interval, is introduced to allow time forstanding 5 trafllc to get into motion. While not essential to operationthis initial interval is preferably introduced to increase theeiilciency of the system. After the expiration of the initial intervalthe go signal will continue to be displayed for 5 vehicle to progressfrom the trafflc detector thru the intersection. This last namedinterval has been identified above as the "vehicle interval"; During the"vehicle interval" the actuation of a tramc detector in the lane inwhich the "go" signal is being displayed extends the right of way periodtherein for a time interval reasonably suiiicient to allow the vehiclewhich actuated the traiilc detector to progress from said detector thruthe intersection.

The system disclosed herein however includes a new and important featurein that the timing of the vehicle interval is affected by the number ofwaiting vehicles in the cross lane as mentioned before so that as thegroup of waiting vehicles increases in number the control will takeadvantage of shorter and shorter breaks in the moving trailic totransfer right of way to these waiting vehicles.

Furthermore this system includes another new feature in that it providesthat if desired certain forms of traflic such as trolley cars, fireapparatus, etc., to which it may be advisable to accord preferredtreatment can thru actuating special detectors have the same eflect onthe timing of the.signals as several ordinary vehicles.

This system, like some previous trai'ilc actuated systems is arranged sothat the timing of the "initial interval", the first part of the "go"period, can, before the beginning of said "initial interval, bepreadjusted between a predetermined minimum value and a predeterminedmaximum value, by successive actuations of the traiilc detector in thelane in which the stop" signal is being displayed so that when said laneshall next be given the g0" signal the initial interval" of said go"signal display period will be timed in conformance with the volume ofthe traillc waiting in said lane, to the end that a large number ofwaiting vehicles will be granted a longer initial interval than will begranted to a small number. However in the system described herein thevariable initial interval is achieved by a method using simpler and morereliable equipment than that used in previous systems, as will be morespecifically shown later.

In this system the traflic detectors can be located at a distance fromthe intersection customary in the prior systems but it is entirelyfeasible, especially if the variable initial interval is employed, tolocate them considerably farther from the intersection (two or threehundred feet or more for example) thereby facilitating the counting oflarger numbers of waiting vehicles which will increase the effectivenessof trafllc approaching a stop signal in controlling the signal timing.

With the system adjusted to give a pronounced reduction of the vehicleinterval after the accumulation of a certain amount of traflicapproaching a stop signal a considerable degree of coordination betweenadjacent intersections can be obtained solely by the pressure of trafllcitself without any electrical interconnection since the effect of agroup of vehicles approaching successive intersections equipped withthis system will be to so reduce the vehicle interval for cross traflicat each intersection as at any time subsequent to the cross streetinitial interval to practically seize the right of way at intersectionafter intersection thereby favoring uninterrupted progress to asufliciently large compact group of vehicles.

Cross traflic will however be protected against 9,183,780 an interval oftime at least sufficient for a moving unreasonable interruption since'the cross street initial interval is timed in advance in accordancewith the number of vehicles waiting on the cross street and is notreducible by main highway trafflc, and in addition either a maximumlimit to right of way on the main highway or a reduction of the mainhighway vehicle interval by accumulation of waiting cross streettraiiic, or both, serve to protect the cross street traffic.

The coordination effect outlined above will be obtained by a compactgroup oi vehicles whether they move along one street or follow anirregular path through an area which is a considerable advantage overprior non-vehicle actuated coordinated systems in which coordination wasnecessarily arranged to favor the passage of trafflc along apredetermined route.

Under this system while a compact group of vehicles is crossing itspath, scattered traffic is automatically given the opportunity to comeinto close order through a natural accumulation. Hence when this systemis applied to a large area constituting a grid of individually andindependently controlled intersections trafflc will form into compactgroups at the outlying intersections and then pass thru the grid asfavored units thereby causing the controls throughout the whole area tofunction as a coordinated grid system without the necessity for anyelectrical interconnection between intersections.

It will be appreciated that traiiic is often heavier inbound toward thecentral area of a city in the morning and heavier outbound in theafternoon, and that in such cases the automatic natural coordinationeffect above noted with this invention will be particularly pronouncedon the main traffic arteries.

It is an object of this invention to provide an improved traflic controlsystem wherein the functioning of the apparatus will automatically takeinto account the relative densities of traillc in the two roadways indetermining the signal timing.

Another object is to provide an improved sysin which the right of asingle vehicle or a scattered group of vehicles to pass the intersectionis not by any means permanently withheld. A single waiting vehicle willbe given an opportunity to pass within a reasonable period after itsapproach to the intersection even though moving cross trafllc may becontinuous. If there is no cross trafl'ic such a vehicle will be giventhe right of way immediately upon its approach?- It is another object toprovide a system in which vehicles awaiting the right of way in one lanewill facilitate yielding the right of way from the other roadway byreducing the time allotted to each vehicle entering the intersectionfrom such other roadway.

It is a further object to provide a system in which vehicles awaitingthe right of way in one roadway will reduce substantially in proportionto the number of said waiting vehicles, the time allotted to eachvehicle entering the intersection from the other roadway in which thego" signal is being displayed thereby automatically permitting a largeamount of waiting traflic to take the right of way more easily than asmall amount.

It is also an object of the invention under some conditions to reducesubstantially the vehicle protection interval on one street aftersuiilcient traffic has accumulated on the opposite street.

It'is another object of this invention to pro- -tem in which the densertrafllc is favored, but 5 voiume 'preadiust, by controlling the startingpoint, the: timing 'of the following. preliminary right of way period. 4i

It is afurther object 'to provide a system in which waiting traiiicwillautomatioally-and substantially in proportion to its'volumepreadjust I theduration of the following right of way period by changingthe starting point of this timing period in accordance with the numberof ve-f I hicles approaching the intersection against the stop signal.

.go" period. 1

1 It is also an obiectiof this invention to provide a system in whichthe variation of charge in a condenser .is instrumental in timing thegoi periods and in which vehicles approaching the .intersection againstthe stop signal will preadjust the timing of thefollowing "go" periodthru varying in accordance with the number of such vehicles the initialcharge in said, condenser at the beginning of the said following It isanother object to provide an improved system in which the right of waywill be automatically returned to a traflic lane later if said right ofway was last withdrawn from that lane by the maximum timer less than apredetermined time after the last traffic actuation of a detector inthat lane.

It is still another object to provide a system in which the right of waywill automatically be returned to a traflic lane at the first reasonableopportunity if, when the right of way is withdrawn, the vehicle intervalallotted to vehicles in that lane is thru the action of waiting crosstraflic or .otherwisedecreased to less than a predetermined time period.

Another object is to provide a system which can be arranged sothatseveral adjacent intersections under this type of control willoperate as a coordinated group or grid so as to facilitate the formationand passage of a large compact group of vehicles thru this group or gridin any path solelythru the pressure of traflic without any electricalinterconnection among the intersections. a 1

It is also an object to provide a system in which if desired certainforms of traiilc such as fire apparatus or trolley cars can have amultiple effect in timing the signals so that one actuation by such avehicle can have the same effect as several actuations by ordinaryvehicles -The invention is designed to encourage the closing up ofscattered traflic which may wlshto cross the path of dense traflicthereby effecting high emciency in the use of one intersection or agroup of intersections. However such scattered trafiic is never forcedto come into close order unless the right of heavier cross trafllcrequires this procedure. Hence the system operates to procure thegreatest good to the greatest number without unduly sacrificing therig-ht of any.-

The invention is exemplified in and will be particularly described inconnection with the accompanying drawings, in which:

Figure 1 is a plan view of an intersection showing the location oftraflic detectors, signals and timer housing.

Figure 2 is a plan view of a group of adjacent intersections equippedwith this system showing one example of the location of signals, trafllcdetectors and timer housings.

Figures 3 and 4 together comprise a circuit diagram of one form ofapparatus embodying my invention including apparatus with an- ,nectionsto and t'railic detectors.

Figures 5 and 6 show a circuit diagram for an alternative and in somerespects preferred form of apparatus embodying my invention and.employinga somewhat diiferent form of timing apparatus with itsconnection to signals and traiiic detectors.

Figure 7 is a schematicdiagram of a form of specialdeteetor equipment bymeans of which preferred tramc can exert a multiple'ei'fect on thetiming apparatus.

' The traillc detectors for'each'intersection in used in this system butthe customary red, yellow and green traflic lights are preferableinasmuch as motorists and pedestrians are now generally familiar withthe significance of these colored lights. s

'The trafilo detectors may be of any desired form such as a mechanicalswitch in which the pressure exerted by the weight of a passing vehicleflexes a resilient plate to make a contact, or an energy beam isdirected across atraflic lane so as to be interrupted by trailicapproaching the intersection. A common form of the latter type is alight beam directed across a trafiic lane with a photoelectric cellarranged as a receiver. .Still another-type of detector isv-anelectromagnetic device in which the vehicle disturbs a magnetic fieldand thereby operates a relay in the control Any of these or other typesof traflic detectors such as a push button for use of pedestrians willoperate satisfactorily in this system.

The timermechanism shown in Figs. 3 and 4 herein which controls thesignals and is responsive to the trailic detectors is of the type inwhich cams, fixed on a shaft which is revolved in steps by a solenoidwith a ratchet and pawl mechanisrn or" other suitable means, operatecontacts to control the signal indications and to connect the varioustiming units in the timer circuit .properly for'th'e particular point inthe signal cycle prevailing.

The cam shaft used in this system employs eight steps to complete onerevolution which carries the signal indication thru one complete cycle,that is, from a go indication in one lane thru the go indication on thecross lane and thence back to the go indication on the firstlane;

In the embodiment shown in Figs. 3 and 4 the timing of the variousintervals is accomplished by means of apparatus including three elementthermionic tubes arranged to be influenced by traflic approaching theintersection. A direct current relay is connected in the plate circuitof each tube in such a way that. the plate current passes thru anoperating coil of this relay. With A condenser is included in each gridcircuit. The voltage of each grid is controlled by the charge on thecondenser associated therewith. When a grid condenser is suflicientlycharged, the plate current will become great enough to operate the relaythru which it Hence by controlling the starting charge and the rate atwhich charge is added to or subtracted from the grid condenser, eachtube can be made to operate the relay associated with it at the end of alonger or shorter period. I

Figures 3 and 4 are complementary. In both figures the contactsidentified by the capital letter C followed by a numeral are operated bycams mounted on a common cam shaft. This shaft is rotated by action ofthe solenoid 3 shown schematically in Fig. 4. The contacts identified bythe letter 8 followed by a numeralare operated directly by the solenoid8. Each time the solenoid rises in its stroke each of these contacts ischanged from its normal condition of closed or open to the oppositecondition. As the solenoid returns to its position of rest thesecontacts return to their normal unoperated conditions. Each cycle ofoperation of the solenoid including forward stroke on energization andreturn stroke on de-energization rotates the cam shaft thru degrees.

Eight steps of the shaft complete one revolution during which thesignals 4! to ill inclusive in Fig. 3 go thru one complete cycle ofchanges, i. e., from green in one street thru green in the cross street,back to green in the first street. The table at the bottom of Figure 4indicates which cam contacts are closed in each of the eight positions.of the cam shaft. An X in a square indicates that the contact whosenumber is at the top of the particular column including that square isclosed when the shaft is in the position identifled by the number at theend of the horizontal row passing thru that square.

The cam shaft positions are numbered from i to 8 as indicated in thetable in Figure 4. When the cam shaft is in positions 1, 2 and 3 thegreen signal 45 is displayed to N-S trafllc, when in position 4 theamber or warning signal 48 is displayed to N-S traillc, and when the camshaft is in positions 5, 6, 7 and 8 the red signal 41 is displayed to NS trailic. The EW green signal 48 is displayed while the cam shaftoccupies positions 5, 6 and 7, the EW amber signal 49 is displayed incam position 8 and the EW red signal in cam positions 1, 2, 3 and 4.Other signal display sequences can of course be provided by thisapparatus but this particular one is cited because it is in quitegeneral use in tramc control systems.

In Figures 3 and 4 negative power is supplied thru the wire designatedby a minus sign enclosed in a circle and a square which common groundednegative for both D. C. Positive A. C. is supplied through wiresdesignated by a plus sign in a circle, and positive D. C. thru wiresdesignated by a plus sign in a square.

Referring to Figure 3, the apparatus represented by that part of 'thedrawing to the right of the. negative power wire is in general eflectiveto cooperate with the apparatus of Fig. 4 to call the right-of-way tothe EW lane and to hold the right of way thereon. In like manner theapparatus represented by that part of Fig. 3 to the left of the negativepower wire is effective to cooperate with the apparatus of Fig. 4similarly to call or hold the right of way on the N-S lane.

signifies a low and red lights.

At the top of Fig. 3 are shown the two sets of signals representing thecustomary green, yelnumbers 48 to II being displayed to the EW tramcwhereas numbers 4| to 41 are displayed tothe NS traffic.

The traffic detectors located respectively in the N-HS and EW lanes arerepresented by II and 5!. Relay E is responsive to actuations ofdetector II and relay 1" operates in response to actuations of detector52.

The operation of relay F starts a sequential operation which calls theright of way to the E-W lane and when the right of way has been given tothe EW lane, operation of this relay tends to hold it there. Similarlyrelay E operates to call and hold the right of way on the N-S lane.

Relay M cooperates with relays E and F in calling the right of way asmentioned above and is also effective thru cooperation with relay A anda contact of solenoid S to cause right of way to return to a given lanelater if, when right of way last left this lane the vehicle protectioninterval was shorter than a predetermined period, or if a detector wasactuated thus initiating a new vehicle interval in this lane within apredetermined time previous to the yielding of the right of way to thecross lane.

Relay C cooperates with tube CT and condenser KC to time all theintervals which remain constant during successive signal cycles such asthe amber period for each lane (cam shaft in position 4 or 8) and themaximum period during which trafllc can hold the right of way on eitherstreet against a cross lane call (cam shaft in position 3 or 1). Inaddition if switch 69 is closed relay C, tube CT and condenser KC willcooperate to call the right of way to the E-W lane a predetermined timeafter said right of way last left the EW lane, and closure ofswitch itwill in a like manner cause relay C, tube CT and condenser KC to callthe right of way to the N-S trafllc lane a predetermined time after theright of way last left the N-S lane. This effect is termed the periodiccall".

By opening or closing switches 68 and 68 the apparatus can be caused tonormally operate as a reverting,,arterial or floating system. Theclosure of both switch 68 and switch 69 will in the absence of trafliccause the right of way to normally revert periodically from lane tolane. This system of operation is commonly called the reverting system.

If switch 68 is closed and switch 89 is open a NS arterial systemresults in which the right of way will normally remain on the NS lane.until called by trafllc to the EW lane. After the EW trailic hascleared the intersection Q the right f W y will automatically revert tothe N-S lane. In the event of continuous EW traflic under the abovesystem the right of way will periodically revert to the NS lane, andremain there as long as N-S traflic may require it up to a predeterminedlimit.

If switch 59 is closed and switch 68 open the system will operatearterial EW under which system the EW lane instead of the N-S lane willbe the artery. The right of way will normally remain on the E-W laneuntil called by tramc to the NS lane, from which lane it will revert tothe EW lane when the N -S traffic has cleared the intersection or hasheld the right of way on the N-S lane for a predetermined time.

If switches 63 and 69 are both open the apparatus will operate as afloating system under which the right of way will normally remain on thelane to which it was last called until traffic on the cross lanerequires it.

Under all of these systems of operation traflic on each lane can holdthe right of way up to a predetermined period against waiting traffic inthe cross lane and in addition automatically put in a call for thereturnof the right of way to the lane from which it is being transferredii at the time of such transfer a'vehicle interval has been initiated bya detector actuation in said lane within a predetermined time prior tosaid transfer of the right of way or if the vehicle interval prevailingthereon at the time of such transfer has by waiting cross traffic beenreduced to less than a predetermined magnitude.

The cooperative action of relay C, tube CT, and condenser KC which timeall intervals which do not vary from cycle to cycle is as follows:Condenser KC during each of these various intervals is being chargedthru a fixed resistance, one of the several indicated in the right orleft side of Fig. 3. As this charge increases the voltage of the gridct2 of tube CT to which condenser KC -is connected increases. Hence theplate current of tube CT increases. When this current reaches asuflicient magnitude relay C operates which in turn operates thesolenoid S to move the cam shaft into its next position.

In a generally similar manner tubes AT and BT are associated withcondensers KD and KB and with relay B, which is a double coil relay, totime the initial and vehicle intervals which vary in their timing fromcycle to cycle in accordance with the requirements of traffic. Coil D3of relay B is its main operating coil. Coil b2, the bucking coil, isconnected so that its magneto-motive force opposes that of coil b3 andtherefore modifies the effectiveness of coil b3 to operate'relay B. Inorder to insure that the bucking coil b2 shall under no circumstancesoperate relay B its magneto-motive force should always be less than thatrequired to operate relay B or as an alternative said relay B might beof the polarized type in which case no limit need be placed on themagneto-motive force of coil b2. Current flows thru coil I)! only whenthe cam shaft is in position 3 or 1, the NS and EW trafiic timedpositions, since in all other positions of the cam shaft the grid oftube ET is biased negative to such a degree that substantially no platecurrent flows in this tube or in coil b2 of relay B.

With the cam shaft in position 3 or I the current thru the bucking coilD2 is regulated in accordance with previous actuations of the de-'tector in the lane in which the stop signal is displayed, in such a waythat this current is caused to be less than a predetermined maximum byan amount substantially in accordance with the volume of the waitingcross traffic. This effect is the means by which waiting cross trafficdecreases substantially in accordance with its volume the timing of thevehicle interval in the lane in which the go" signal is being displayed.

The current thru operating coil 173 when the cam shaft is in position 3or 1 is affected by actuation of the detector in the lane in which thego" signal is being displayed in such a way that a new vehicle intervalis initiated for each actuation of a detector in this lane. Therefore itcan be seen that traffic in both lanes affects the operation of relay Bto time the vehicle interval for each lane in accordance with the traftocontrol the effectiveness of tube ZBT in modi-' fying the operation ofrelay B to the end that waiting cross traflic can be caused to have agreater or less effect on the timing of the vehicle interval. In anetwork of intersections equipped with this system these by-passresistances could be adjusted to a high value in order to increasemarkedly the effect of waiting cross traffic in decreasing the vehicleinterval to aid in emphasizing the coordination effect naturallyinherent in a group of adjacent intersections equipped with thisapparatus.

Tube AT, as mentioned above, also cooperates thru the coil of relay Awith coil D3 of relay B, condensers KE and KD, to time the initialintervals, cam shaft position I or 5, substantially in proportion to thenumber of vehicles waiting in the lane in which the go signal isdisplayed at the beginning of such interval. During the initialintervals coil D2 of relay B carries no current due to the negative biasof gridbt2 of tube ET. Hence coil b3 alone is effective to control relayB during the initial intervals.

Relay A is effective to cooperate thru solenoid and cam shaft contactsS2, C5, and C6 to operate relay E or relay F which will in turn operatethe memory relay M to call the right of way to the lane from which it isbeing transferred if, at the time of such transfer, the vehicle intervalprevailing on said lane is less than a predetermined time or if theright of way is transferred by action of the maximum timer less than apredetermined time after a vehicle interval has been initiated by adetector actuation in said lane from which the right of way is beingtransferred. If either of these named conditions prevail relay A will beunoperated at the time the cam shaft moves into position 4. Thereforeduring this movement armature al of relay A thru its back contact andsolenoid contact S2 complete a recall circuit to operate the memoryrelay M and thus cause the right of way to return later to the lane fromwhich it is being transferred just as if a vehicle detector in this lanehad been actuated.

To more completely explain this system I shall now described in detailits operation to carry the signals thru one complete cycle.

Relay E is operable in all cam shaft positions upon actuation of the NSvehicle detector 5| which completes a circuit from negative power, thrudetector 5| and wire 59 to the coil of relay E thence to positive power.Similarly relay F is operable in all cam shaft positions upon actuationof the EW vehicle detector 52 which completes a circuit from negativepower thru detector 52 and wire 60 to the coil of relay F thence topositive power. The effect produced by the operation of these relays isdifferent in different cam shaft positions as will be pointed out in thefollowing description of the operation of the system.

Assume that the cam shaft is in position 2, called the NS rest position.The NS go signal is energized thru wire 53 and cam contact C38. The EWstop signal is energized thru wire 58 and cam contact C39. Condenser KEwhich cooperates with tube AT and relay B to time the NS vehicleinterval is being charged thru the following circuit. Positive powerthru resistance R4, contact Cl5, wires 85 and 80 to condenser XE thenceto negative power. -While thecamshaftisinposition 2condenserKEis subjectto discharge at each vehicle actuation of detector 2i thru the operationof relay 3. The subsequent recharge period of condenser KE constitutesthe vehicle interval for the passage thru the intersection of thevehicle in the 21-8 lane which caused the operation of relay E. Thisdischarge circuit for condenser KE goes from negativepower to armaturec2 of relay E, wires I2, 2|, contact CI2, wires 22 and 22 thru condenserKE and thence back to negative power.

In this cam shaft position condenser KI: which as before mentionedcooperates with tube AT and relay B to time the NS vehicle interval isconnected to the grid at2 of tube AT thru wires 22, 22, contact CI2 andwire I22. Hence the voltage of condenser K1: is effective to control theplate current of tube AT. This plate current passes thru coils of relaysA and B thru a circuit starting at negative power, thru potentiometerresistance PI, wire II2, filament MI and plate at2 of tube AT to relay Athence thru wire III to coil b2 of relay 3 to positive power. Coil b2 ofrelay B carries no current while the cam shaft is in position 2 sincethe grid N2 of tube BT is biased sufllciently negative with respecttofilament bfI thru wires I2l, I22 and contact CI2 to prevent any platecurrent from flowing in tube BT. I

When condenser K1: is charged to a sufficient voltage the plate currentof tube AT which passes thru coil b2 will be great enough to operaterelay 8. When condenser KI: has further charged to a still higherpredetermined voltage the plate current of tube AT will further increasethus causing relay A to operate. While the cam shaft remains in position2 the operation of relay A or relay B is of no effect since theirarmatures whether operated or not operated do not affect any circuit.Relays A and B will however function when the cam shaft has moved intoposition 2 as will be explained later.

Movement of the cam shaft into position 2, called the N-S trafllc timedposition, is made in response to a cross lane call resulting either froma vehicle actuation of the E-W detector 22, or by action of the E-Wperiodic call circuit if the system is set to normally revert to the E-Wlane, as would for instance be the case if the system were set to revertperiodically from street to street or if the i l-W lane were the mainhighway of an arterial system.

An E-W detector actuation will cause this cam shaft movement as follows:The operation of the E-W detector 22 will complete the circuit of relayF from negative power to positive power thru wire 22. The operation ofrelay 1'' will energize relay M thru a circuit starting at negativepower thru armature 12 of relay F, wires 22, 22, contact CII, wire 22 tocoil of relay M thence to positive power. Relay M will thereupon oper-'-ate and lock in thru the circuit starting at negative power thence thruarmature ml of relay M, wire 22, contact CI2 and coil of relay M topositive power. Solenoid S will now be energized thru a circuit fromnegative power thru armature ml of relay M, wire 22, contact CI2, wireI28, armature s2 and coil of solenoid S to positive power, Solenoid Swill therefore operate andcause the cam shaft to move into position 2.

With the system set to operate normally as a reverting or EW arterialsystem switch 62 would be closed so that if no actuation of an E-Wvehicle detector takes place the cam shaft, after remaining in position2 for a predetermined time. will be moved into position 2 by action ofthe periodic call circuit as was previously mentioned.

The movement of the cam shaft to position 2 by means of the periodiccall circuit is accomplished as follows.-

With switch to closed condenser KC is charging while the cam shaft is inpositions I or 2 thru the circuit starting from positive power reach amagnitude sumcient to operate relay thru its circuit starting atpositivepower thru the coil of relay C and wire I22, plate ct2, and

' filament ctI of tube CT, wire I I2, potentiometer resistance PI tonegative power. The operation of relay C will complete the circuit fromnegative power thru armature cI of relay C, wire I22, 22, contact C22,wire 22, coil of relay F, thence to positive power. Relay F will nowoperate and cause relay M to operate solenoid S as before explained tomove the cam shaft into position 2.

By adjusting the variable resistance R2 the time required to chargecondenser KC up to a voltage sufficient to cause the operation of relayC as above described'can be made greater or less. Since condenser KCstarts to charge when the cam shaft moves into position I and E--Wperiodic call can be made to cause the cam shaft to move from position 2to 2 at any predetermined time after the NS lane is given the go signalunless Iii-W traflic has previously caused said transition. ResistanceR2 in a similar manner regulates the timing of the N-S periodic callwhen the cam shaft is in position 2. It is by closing switches 62 and 69and properly adlusting variable resistances R2 and R2 that the right ofway as before mentioned can be made to normally revert at any desiredintervals from street to street in the absence of trafllc.

As the cam shaft moves into position 2 contact CI2 opens thus breakingthe lock-in circuit for relay M which thereupon assumes its unoperatedcondition.

The operation of the solenoid S to move the cam shaft from position 2 to2 is as follows. When the solenoid S is energized, as explained above,the core moves into the solenoid. The first effect of this movement isto change each of the solenoid contacts SI-SI from its rest position inwhich some contacts are made and others open to the opposite conditionwherein those contacts which were made when the solenoid was at rest arebroken and those which were broken are made. As contact S2 opens thesolenoid is deenergized but the inertia of the solenoid armsture carriesit beyond this point a considerable distance. At the top of the stroke apawl engages the cam shaft ratchet so that on the down stroke the camshaft is revolved thru 45 degrees. On the down stroke some cam contactschange before the solenoid contacts return to their .normal positionsand others change after in order to secure the proper sequence in thecircuit changes occurring during this period of transition from one camshaft position to another.

While the solenoid is operating to move the cam shaft from position 2 to2 solenoid contact S2 completes a discharge circuit for condenser KC,which has been timing the periodic call period, to insure that noresidual charge remains arcane therein when condenser KC starts to timethe maximum period in cam shaft position 3. As the solenoid returns toits unoperated position contact SI opens this discharge circuit whichmay be traced from negative power thru contact 33, wire I", contact 01,wires Hi2, ill to'con-' denser KC thence back to negative power again.

While the cam shaft is moving into position 8 and while it remains therethe circuits thru which relay A and coil M of relay B are energized,which have been previously described, re-

' main as they were when the cam shaft was in position 2. As the camshaft moves into position 3 relay B will have been operated if more thana predetermined period of time has passed since the last actuation ofdetector 5| and if relay B remains operated when the cam shaft has,

. coil M as the cam shaft moves into position 3 may, if the current thrucoil b8 has at that time reached a magnitude only slightly greater thanthat required to operate relay B without the opposition of coil b2, besufficient to cause the armature of relay B to temporarily drop out.However the current thru coil b3 continues to increase if there are noN-S detector actuations. When this last named current reaches asufiioient magnitude it will overcome the opposition of coil b2 andcause relay B to again operate and move the cam shaft on into position4.

It is thru the effect of coil b2 on the operation of relay B thatwaiting EW cross traffic decreases the N-S vehicle intervalsubstantially in accordance with its volume. This is accomplished asfollows:

The magnitude of the current thru coil b2 when the cam shaft is inposition 3 is regulated in accordance with. the number of actuations ofdetector 52 since the last display of the go signal in the EW lane,which is substantially a measure of the traffic waiting in the EW lane.This condition is brought about by connecting the grid bt2 of tube BT tocondenser KD in cam shaft position 3. As will later be explained indetail the charge on condenser KD at any time .when the cam shaft is inposition 8, I, 2, 3 or 4 is a predetermined charge, introduced when thecam shaft last moved from position I to 8, less the several incrementsremoved thereafter in positions 8, I 2, 3 and 4 by small condenser K2 inresponse to vehicle actuations of EW detector 52. Hence the voltage ofcondenser KD and therefore the voltage of grid M2 and consequently theplate current of tube BT, i. e., the current flowing thru coil b2 ofrelay B, will be of a magnitude less than a predetermined value by anamount substantially in proportion to the number of actuations ofdetector 52 since the go signal was last displayed in the EW lane. Aswill be later explained in connection with the description of thecircuits for reducing the voltage of condenser KD by increments bycondenser K2 the amount of this reduction will be independent of thespeed of individual E-W vehicles but will depend only upon the number ofactuations by such vehicles.

Since a reduction of the current in coil b2 facilitates correspondinglythe operation of relay B-by the current in coil his. smaller currentincoil M will be suflicient to operate relay B. A

which controls the current thru coil bl, will be s'ufllcient to'producethis smaller current in coil bl. Since this smaller charge willaccumulate in condenser Kit in a proportionately shorter period thanwould be required for a greater charge the vehicle interval being timedby this relay will. because of the sequential effects described, bedecreased in accordance with the reduction of the current in coil 122.Since the reduction of the current in coil b2 is, as above stated, inaccordance with the volume of waiting EW cross traflic the reduction ofthe N-S vehicle interval will consequently also be in accordance withthe volume of waiting E'W cross traffic. I

The proportion of the plate current of tube BT passing thru coil D2 ofrelay B with they cam shaft in position I-is regulated by adjustingresistance Rll in order, as before mentioned, to increase or decreasethe effectiveness of waiting EW vehicles to reduce the N--S vehicleinterval. circuit including resistance R, wire 81, contact C26, and wire88 accomplishes this effect by bypassing around coil D2 of relay B aproportion of the plate current of tube BT determined by the value ofresistance RI I.

The circuit for the charging of condenser KD during the movement of thecam shaft from position I to 8 as mentioned above will be traced whenthe transition of the cam shaft from position I to 8 is described. Thecircuit by which this charge is diminished by vehicle actuation of EWdetector 52 occurring while the cam shaft is in positions 8, I, 2, 3 orI is traced as follows.

When relay F is unoperated condenser K2 is charged from condenser KDthru the circuit starting from negative power thru potentiometerresistance P3, wire 16, condenser K2, wire H, ar-

The.

mature fl of relay F, wire 12, contact C25, wire 86, 9|, condenser KDthence back to negative power. An actuation of detector 52 will, asbefore explained, operate relay F which will break the last describedcircuit at armature j I of relay F thus disconnecting condenser K2 fromcondenser KD. Furthermore the operation of relay F will establish adischarge circuit for condenser K2 as follows, condenser K2, wire H,armature f2 of relay F, wire I8, potentiometer resistance P3 and wire16. As the vehicle releases detector 52, relay F becomes de-energizedthereby breaking the discharge circuit for condenser K2 and reconnectingcondenser K2 with condenser KD from which it will again be chargedthereby removing another increment of charge from condenser KD. Asindicated before, condenser K2 is of considerably smaller capacity thancondenser KD and therefore each actuation of relay F by an EW vehiclereduces the charge and corresponding voltage of condenser KD by only asmall increment. Also such reduction of charge on condenser KD by aseries of EW actuations is arranged to take place on a relativelystraight portion of the natural discharge-time curve of the condenserKD. Thus successive actuations reduce the charge on condenser KD bysubstantially the same amount and the total amount cof reduction by aseries of actuations is substantially proportionate to the number ofactuations in such series. It will be, appreciated that small condenserK2 will be substantially fully charged each time it is connected tolarge condenser KD by actuation of relay F, and then condenser K2 willbe substantially discharged upon de-energization of relay F by cessationof such actuation and therefore the amount of charge removed fromcondenser KD by each such actuation will be independent of the timerelay F is energized bysuch actuation and consequently will beindependent of the speed of individual actuating vehicles.

The magneto-motive force of coil M which as before explained opposesthat of coil b3 is always considerably less in magnitude than that ofcoil 123 since it is intended merely to serve to fix the currentrequired in coil hi to operate relay B.

The more vehicles waiting in the EW lane the less will be the current incoil b2 when the cam shaft is in position 3 as previously explained,hence a correspondingly lower current in coil-bl will operate relay B.Since the charge in condenser KE which controls the current thru coil b3in cam shaft position 3 will be built up more quickly to the lower valuerequired to produce this lower current in coil b3, the vehicle intervalbeing timed thereby is therefore decreased substantially in proportionto the number of vehicles waiting in the EW lane.

The circuit by which condenser KD is connected to grid bt2 is fromnegative power to condenser KD, wire SI, 93, contact C23, wires I20 andI2l. Contact Cl9 thru which grid M2 is usually biased negative is openwhen the cam shaft is in position 3.

The circuit by which relay B operates the solenoid S to move the camshaft to position 4 is from negative power thru contact Ctl, wire I23,armature bl of relay B, wire I26, armature s5 and coil of solenoid S topositive power.

While the cam shaft is in position 3 condenser KE is, as previouslymentioned, subject to discharge by actuation of N4 detector M in orderthat each vehicle entering the intersection from the NS lane mayinitiate a new vehicle interval to permit its passage thru theintersection. If vehicles in the N-S lane approach at sufficiently shortintervals they may by repeatedly discharging condenser KE keep itsvoltage so low that tube AT will not at any time pass current enough tooperate relay B. In order to insure that a continuous line of traflic inthe NS lane cannot thus indefinitely hold the right of way another meansfor moving the cam shaft into position 4 is provided in the maximumtimer, the operation of which is not affected by trafllc.

The maximum timer as before mentioned is comprisedof relay C, tube CT,condenser KC and resistance R2. Relay C when operated in cam position 3is affected to move the cam shaft into position 4 thru the followingcircuit, negative power, armature cl of relay C, wire I25, contact C30,wires I24, I26, contact s5 and coil of sole-- noid S to positive power.Condenser KC is connected to grid ct! of tube CT by wires I03, Ill andI04, and is charged in cam position 3 thru a circuit from positivepower, contact C34, resistance R2 and wire Ill. Resistance R2 isadjusted to charge condenser KC at the proper rate to operate relay C apredetermined time after the cam shaft has moved into position 3 hencethis timer circuit will be effective as a maximum timer to move the camshaft into position 4 at the end of this predetermined period ifcontinuous N-S trafllc has prevented relay B from doing so earlier. I

If relay A is unoperated as the cam shaft moves from position 3 to 4 itwill put in a N-S return call by causing operation of relay E, just asif a vehicle were to actuate detector!" at that intransition to position4 took place.

stant. The circuit by which relay A determines operation of relay E isfrom negative power to armature al and back contact of relay A, wireIll, wntact :2 of solenoid 8, wire 63, contact C4, wire II to coil ofrelay E thence to positive power. Contact C4 is closed only in ,camposition I and contact 82 is closed only while the solenoid is in itsoperated position, hence this circuit is completed if relay A isunoperated while the solenoid is in its operated pofltion preparatory tomoving the cam shaft into position 4 which it will do as it returnsto'its unoperated position.

Relay A will be unoperated and will therefore thru the above circuit putin a N-S return call as the cam moves into position 4 ii as beforestated the vehicle interval then prevailing has by waiting EW traffic orotherwise been decreased to less than a predetermined time, or if thelast N-S vehicle interval was initiated less than a predetermined timebefore the said cam shaft In the above description of the two conditionsunder which a return call will be put in, the predetermined timementioned is fixed by the operating period of relay A. This can be seento be true because of the following facts.

In cam shaft position 3 the operation of relay B, which times thevehicle interval, or of relay C, the maximum timer, will be effective tomove the cam shaft on into position 4 and thus extinguish the NS gosignal and illuminate the N-S amber or warning signal. If relay Aoperates before either relay B or' relay C operates no N-S return callwill be put in since contact al will be broken when the solenoidoperates but if relay A does not operate before the cam shaft is movedinto position 4 by action of either relay B or relay 0 a N-S return callwill be put in during this transition. Whether relay A operates beforeor after relay B or relay C depends upon circumstances involving thefollowing factors.

Relay A always operates when the current thru its coil reaches apredetermined value which, in cam position 3, always occurs apredetermined time after the last vehicle actuation of a N-S detector.Relay B always operates when the difference betwen the current in coilsb2 and b3 reaches a predetermined magnitude which condition occurs at atime after the last vehicle actuation of a N-S detector dependent uponthe current in coil b2. Hence, although the same current passes thrurelay A and thru coil b! of relay B, relay B may operate either beforeor after relay A dependent upon the effect of the current flowing thrucoil M on the operation of relay B. If the operating period of relay Bby action of waiting cross traiilc on the current thru coil b! isdecreased to less than that of relay A, the return call will be put in.But if the operating period of relay B is not so decreased and isconsequently longer than that of relay A no return call will be put inif the cam shaft movement is caused by relay B. Hence the operatingperiod of relay A constitutes the predetermined period below which thevehicle interval must be reduced by waiting crtms traflic in order toput in a return call. If on the other hand the cam shaft is moved intoposition 4 by action of the maximum timer relay C less than apredetermined time after'the last detector actuation in 7 cam shaft intoposition 4 condenser KE, preparatory to timing the next N-S initialinterval 7 and preparatory to decreasing the E-W vehicle intervals inaccordance with the waiting NS cross traiiic, is charged to apredetermined voltage thru a circuit starting at negative power thenceto condenser KE, wires 90, 02, contact C4, wire I01, contact sl ofsolenoid S, wire I09, contact Cl, wire Ill, potentiometer resistance Plto positive power. The voltage to which condenser KE is charged by thiscircuit can be reg-'- ulated thru setting the point at which wire Illmakes contact with potentiometer Pl.

While the cam shaft is in position 4, 5, 6, I or 8 the charge put intocondenser KE as the cam shaft moved into position 4 is subject todiminution at each vehicle actuation of NS detector by the amountrequired to charge condenser Kl which is discharged and recharged fromcondenser KE once for each such actuation. When the cam shaft nextreaches position I, the NS initial interval position, the rechargingperiod of condenser KE will time that interval thus causing it to betimed substantially in accordance with the number of vehicles waiting atthat time in the N--S lane.

The circuit by which condenser Kl diminishes the charge in condenser KEin response to NS detector actuations is as follows. At each actuationof detector 5i relay E operates as previously explained. While relay Eis operated condenser Kl is discharged to a predetermined voltage thruwire 15, condenser Kl, wire 13, contact e2 of relay E and wire 11. Thecharge left in condenser KI by this circuit is adjustable by setting thepoints at which wires 15 and 11 make contact with potentiometerresistance P2. Each time relay E returns to its unoperated conditioncontact e2 breaks after which contact ei makes thus reconnectingcondenser K! to condenser KE from which it will recharge thru wire 15,condenser KI, wire 13, contact el, wire H, contact C l4, wires 85, 90,condenser KE thence back to negative power.

During the transition of the cam shaft from position 3 to 4 condenser KCis again discharged thru the circuit previously traced thru contact Cland solenoid contact 83 preparatory to its use in timing the NS amberperiod during which period the cam shaft is in position 4. In this camshaft position the NS go signal circuit is opened by contact C38 and theNS amber or warning signal circuit is completed by contact C40.

While the cam shaft is in position 4, the NS amber position, relays Aand B can not operate to move it into position 5 since the grids oftubes AT and BT are biased sufficiently negative thru contacts C20 andC!!! respectively to prevent any ,plate current from flowing in thesetubes which control the operation of relays A and B.

The timing of the NS amber period, during which the cam shaft is inposition 4, is regulated by the charging period of condenser KC whichduring this period is charging thru a circuit starting from negativepower to condenser KC, wires I03, 10, resistance RI and contact C32 topositive power. The duration of the NS amber period can be adjusted byvarying resistance El.

for condenser KC is again completed thru con tact C1 and contact S3 inorder to prepare this condenser for timing the next NS periodic callperiod which it will time while the cam shaft is in positions 5 and 6,if switch 68 is closed as will be the case if the system is operatingnormally as a reverting system or an arterial system with the NS lanethe artery. The charging circuit for condenser KC in cam shaft positions5 and 6 includes switch 60, contact C36, resistance R3, wires Ill andI03. The charging period for condenser KC in cam shaft positions 5 and 6can be regulated by varying resistance R3. When this condenser ischarged to a predetermined voltage tube CT will operate relay C whichwill operate relay E thru contact C28 to call the right of way to the NSlane.

In cam shaft position 5 contacts C39 and C40 open the circuit to the E-Wstop signal 50 and the NS amber or warning signal 46 respectively.Contacts CH and C42 close to complete the circuits to the E-W go signal40 and the NS stop signal 41 respectively. Contact C20 is open whichdisconnects grid at2 of tube AT from negative power and contact C24 isclosed to connect grid at2 with condenser KD. Contact 0 is closed inthis cam position to complete a charging circuit for condenser KD, thruresistance RID, contact C2! and wires 86, 9|. Thru this circuitcondenser KD will be recharged from the voltage to which it had beenlowered by vehicle actuations of the E-W detector while the cam shaftwas in positions 8, I, 2, 3 and 4. This recharge period will besubstantially in accordance with the number of such actuations therebytiming the E-W initial interval in substantial accordance with thenumber of vehicles waiting in the E--W lane at the beginning of thisinterval.

When condenser KD is so recharged to a predetermined voltage tube ATwill pass a plate current thru coil b3 of relay B suflicient to operaterelay B to move the cam shaft into position 6. The operation of relay Bis not in this case affected by coil b2 because the grid of tube ET is,as previously stated, biased negative thru contact Clil to prevent thepassage of any plate cur rent in tube BT. Because of the small currentrequired in coil D3 to operate relay B in the absence of opposition fromcoil b2, relay A does not operate. Moreover, if relay A did operate itwould have no effect since in cam shaft positions 5 and 6 its connectionto relay E and F is broken by contacts C6 and C5 respectively.

As the cam shaft is by action of relay B moved into position 6,condenser K1) is discharged to prepare it for timing the E-W vehicleinterval when the cam shaft is in positions 6 or I. This dischargecircuit starts at negative power thence to condenser m) then thru wires9|, 93, contact C3, wire I08, contact SI, wire H0, contact C2, back tonegative power.

Position 6 is the E-W rest position just as position 2 is the NS restposition. Movement of the cam shaft from position 6 to I isaccomplished, like the movement from position 2 to 3, only thru theoperation of relay M. Relay M will have been locked -in its operatedposition if a vehicle has actuated the NS detector 5i since the gosignal in the NS lane was last extinguished or, as previously explainedin describing the operation of the apparatuswhenthe cam shaft was inposition 3, if either of the following con ditions prevailed when thecam shaft last moved from position 3 to 4:

1. If the right of way was last withdrawn from the 11-8 lane by actionof the maximum timer relay C less than a predetermined time after thelast actuation of a NS detector, or

2. If at the time of this transfer the N--S vehicle interval had beendecreased by waiting EW traflic to less than a predetermined minimumperiod.

If relay M has been locked as a result of the existence of any of theforegoing conditions it will be effective as soon as the cam shaftreaches position 6 to operate the solenoid to move the cam shaft on intoposition 1 thru the circuit which included armature ml and contact CI3previously described in connection with the movement of the cam shaftfrom position 2 to 3.

If relay M has not been operated when the cam shaft moves into position8 this last named circuit will be open at armature ml and solenoid Swill not be energized until relay M is subsequently operated by actionof relay E which can be operated either from an actuation of N-Sdetector 8| or from the action of the periodic call relay C to cause anormal reversion, the circuit for which has been previously described.Condenser KC which cooperates to time the periodic call is, with the camshaft in position ,5 or 8, charged thru the circuit including switch 88,contact C38 and resistance R3. The timing of this NS periodic call, asbefore mentioned, can be adjusted by varying resistance R3.

As the cam shaft moves from position 6 to 1 condenser KC is dischargedthru the circuit including contact Cl and armature 83 of solenoid S toprepare it for timing the maximum period in cam shaft position I. Thecircuit of condenser KC, tube CT and relay C to time this maximum periodis identical with that described in connection with the operation of theapparatus when the cam shaft is in position 3 except that the chargingcircuit for condenser KC includes resistance R1 and contact C35 insteadof R2 and C34.

The EW vehicle interval is timed in position I as the N--S vehicleinterval was in position 3 except that the grid of tube AT is connectedto condenser KD thru contact C24 instead of to condenser KE which makesthe operation of the EW detector 52 instead of the NS detector 5|effective to initiate a new vehicle interval. Furthermore thecounteracting effect of coil D2 of relay B is controlled by the voltageof condenser KE thru contact CI'I instead of by condenser KD, hence thewaiting N-S traffic is effective to decrease the vehicle interval in camshaft position I just as waiting EW traillc de creased the vehicleinterval in cam shaft position 3.

In cam position I resistance RI! thru contact C21 regulates theproportion of the plate current from tube BT flowing thru coil b2whereby the magnitude of the effect of each, NS vehicle actuation todecrease the EW vehicle interval can be controlled.

As the cam shaft moves into position 8 by action of either relay B orrelay C a return call to the EW lane will be put in if relay A isunoperated just as such a call was put in for the N--S lane when the camshaft left position 3 if relay A was then unoperated. The circumstancesunder which relay A will be unoperated when the cam shaft moves fromposition I to 8 are identical with those which would cause it to beunoperated as the cam shaft moves from position I to 4 except that thesecircumstances perta n to conditions caused by EW tramc instead of N-Straflic.

During the transition of the cam shaft from position I to 8 condenser KDis charged to a predetermined voltage which as before stated will in camshaft positions 8, I, 2, 3 and 4 be diminished by vehicle actuation ofEW detector 52 to prepare this condenser for decreasing the N-S vehicleinterval when the cam shaft reaches position 3 and for timing the nextE--W initial interval when the cam shaft reaches position 5. The circuitthru which condenser KD is charged as mentioned during the transitionposition I to 8 is thru wires BI, 93, contact C3, wire I88, armature SI,wire I89, contact CI, wire III to potentiometer resistance PI. Thevoltage of this charge is regulated by the point at which wire I I Imakes contact with PI. The condenser KC is also during this transitiondischarged thru the circuit including contact C1 and armature S3 inpreparation for its use in timing the EW amber period in cam shaftposition 8.

In cam shaft position 8, the EW amber signal position, EW go signal 48is extinguished thru the opening of contact CH and the EW amber orwarning signal 49 is illuminated by the closing of contact C43.

Condenser KC, tube CT and relay C co-operate to time the EW amber periodas they do to time the N-S amber period which has been previouslyexplained in detail. However, the charging circuit for condenser KC incam shaft position 8 includes resistance R8 and contact C33 instead ofRI and contact C32 which are a part of the corresponding circuit in camshaft position 4. The duration of the EW amber period can be regulatedby adjusting resistance R6.

As the cam shaft moves from position 8 to I, condenser KC is againdischarged thru the circuit including contact Cl and armature S3 toprepare it for timing the EW periodic call which it will do in campositions I and 2 if switch 83 is closed as previously explained.

The NS initial interval, cam shaft position I is timed substantially inaccordance with the number of waiting vehicles in the N-S lane bycondenser KE cooperating with tube AT and relay 3 exactly as the EWinitial interval was timed by the same tube and relay cooperating withcondenser KD. Condenser KE, it will be remembered, was charged to apredetermined voltage as the cam shaft moved from position 3 to 4 whichcharge has in cam shaft positions 4, 5, 6, I and 8 been diminishedsubstantially in accordance with the number of vehicles actuating theN-S detector 5i. Hence, as previously explained, the duration of the N-Sinitial interval which is governed by the time required to rechargecondenser KE will be substantially in accordance with the number ofvehicles waiting in the N-S lane at the beginning of this interval.

As the cam shaft moves into position I the EW amber signal 43 isextinguished by the opening of contact C43, and the N--S stop signal 49is extinguished by the opening of contact C42. The N--S go signal 45 isilluminated by the closing of contact C38, and the EW stop signal 58 isilluminated by the closure of contact C39.

As the cam shaft moves from position I to 2 condenser KE is dischargedthru the circuit including contact C4, armature sl and contact C2 toprepare it for timing the N-S vehicle interval in cam positions 2 and 3.

The movement of the cam shaft into position 2 completes the signalcycle.

Stated briefly, intervals are timed by this first embodiment of myinvention by charging or discharging condensers KC, KD and KE. CondenserKC times those intervals which are unaffected by traflic and do not varyfrom cycle to cycle.

The charge in condenser KD is influenced\by E-W traflic actuations andis instrumental in timing the signal display periods in accordance withthe requirements of E-W traflic. The charge in condenser KE is similarlyinfluenced by NS trafflc actuations and is instrumental in timing thesignal display periods in accordance with the requirements of N--Strafllc.

During the N-S initial interval, cam shaft in position I, condenser KE,which has since the last N-S traflic timed period been subject to theremoval of unit charges by each N-S trafllc actuation, is now subject toregular charging action, not reset by actuation, to time the initialinterval by recharging from. that point to which it has been dischargedby such removal of unit charges.

During the E-W initial interval, cam shaft in position 5, condenser KDfunctions similarly to time this interval.

During the N-S trafllc timed period of right of way, cam shaft position3, condenser KE is subject to regular charging action to time thisperiod and is subject to reset discharge by each N-S traillc actuationto extend this period by one vehicle interval. At the same timecondensei- KD, which is and has been since the last E-W traflic timedperiod subject to the removal of unit charges by each E-W trafficactuation, serves to govern the length of such N-S vehicle interval.

During the E-W traffic timed period, cam shaft in position I, condensersKD and KE perform similarly except that their functions areinterchanged.

Another and in some respects a preferred embodiment of this invention isshown in Figs. 5 and 6. This second embodiment employs a rotary lineswitch instead of a cam shaft, and grid controlled discharge tubesinstead of the amplifier type three element thermionic tubes. The use ofthe grid controlled discharge tubes makes it uhnecessary to employ adouble coil relay to permit waiting cross trafllc to decrease thevehicle interval as will subsequently be explained. Furthermore becauseof the sharply defined "breakdown voltage of this type of tube greataccuracy is possible in timing the various intervals. Moreover sincetheir grid potential determines their breakdown voltage the circuitsinvolving these tubes can be adjusted to compensate for variations intube characteristics by connecting the grid to an appropriatepotentiometer tap when tubes are replaced. Thus the accuracy of thetiming of the various intervals can be maintained independent ofvariation of tube characteristics in different replacement tubes.

The stepping switch shown in Fig. 5 has eight positions just as did thecam shaft of Figs. 3 and 4. A stepping switch of more than eightpositions can be used as an eight position switch if desired byproviding rapid stepping thru the extra positions in accordance withwell known methods.

The various time intervals correspond substantially in both embodiments.In this second embodiment as in the first the initial interval is timedsubstantially in accordance with the number of waiting vehicles bycharging a condenser during that interval from an initial voltagepredetermined by the amount of said waiting tramc.

When the stepping switch is in its traflic timed positions 3 or 1, threetimers run concurrently.

One of these, the maximum timer, is not subject to vehicle control. Theother two. the variable vehicle interval timer and the normal vehicleinterval timer, are both subject to reset thru plate condenser dischargeby traflic actuations in the lane in which the go signal is beingdisplayed. Hence their periods start simultaneously after each suchreset. The variable vehicle interval timer is subject also to partialcontrol by waiting cross trafilc which decreases its operating period.The normal vehicle interval timer on the other hand is not affected bycross traffic.

The variable vehicle interval timer period is decreased by waiting crosstraflic thru having the grid potential of the tube timing this periodrendered less negative by waiting cross trafilc thus causing said tubeto become conducting at a lower plate voltage which correspondinglydecreases the period required for charging the plate condenser to thislower voltage and so decreases correspondingly the variable vehicleinterval. Hence the larger the amount of waiting cross traflic theshorter the variable vehicle interval will be. From the abovedescription it can be seen that the variable vehicle interval timer ineifect balances the increasing pressure to take the right of way exertedby accumulating waitting traffic on one street against the right of wayretaining effect exerted by moving traffic on the other street. Thelatter efiect may be termed the holding power and is proportionate tothe frequency with which said moving traflic resets the variable vehicleinterval timer, since moving trafiic having the right of way will resetthis timer at a higher time frequency as the time spacing betweenactuated vehicles is reduced in "the moving stream of trailic, or inother words as the vehicles become more closely spaced. The closer thespacing of vehicles is in the stream of traffic moving with the right ofway the shorter is the time interval between vehicles in which condenserKVV is allowed to charge, and the lower is the maximum voltage condenserKVV is allowed to reach, so that such traffic tends to hold thecondenser voltage below the break down of tube VVT and thus to hold theright of way. This holding power is opposed by the action of trafiicapproaching at a distance on the opposite street, which does not havethe right of way and on which approaching trafiic stops as it reachesthe intersection. Each actuation by vehicles of the latter trafficreduces the negative grid bias on tube VVT and thus reduces its breakdown voltage, so that condenser KVV voltage does not have to rise sohigh to operate tube VVT and cause release of right of way.

If the variable vehicle interval is decreased to less than the normalvehicle interval right of way will be yielded by action of the variablevehicle interval timer when ti'affic ceases to approach the intersectionfrom the lane in which the go signal is being displayed. The variablevehicle interval timer is arranged to automatically put in a returnright of way call whenever it operates to yield right of way. If thereis little waiting cross traffic and consequently the variable vehicleinterval is not reduced to less than the normal vehicle interval, thenormal vehicle interval timer will operate first to yield the right ofway. The operation of this timer does not put in a return right of waycall. Hence in the second embodiment of my invention as in the first, aright of way recall will be automatically put in if the vehicle intervalat the time of right of way transfer has been reduced by waiting crosstraflic to less than a predetermined period. In this second embodimentshown in Figs. 5 and 6 the fpredetermined period" referred to is thenormal vehicle interval timer period whereas in the first embodimentshown in Figs. 3 and 4 the corresponding predetermined period is thenormal period for charging the timing condenser to the voltage necessaryto operate period of relay A. This charging period will be greater thanthat for operation of relay B in the presence of any considerable amountof waiting cross trafllc.

If repeated traflic actuations in the lane in which the go signal isbeing displayed continually reset both of the vehicle interval timersthus preventing either of them from operating the right of way will betransferred by action of the maximum timer, which is effective in thetraffic timed stepping switch positions 3 or 1. A return call for theright of way is automatically put in by this timer whenever it operates.

The fact that the maximum timer operates and the normal vehicle intervaltimer does not operate indicates that the normal vehicle interval timerwas reset by a traflic actuation less than the time period of saidnormal vehicle interval timer, i. e., less than a predetermined timebefore the transfer of the right of way.

It will be remembered that this is one of the conditions under which theembodiment of Figs. 3 and 4 also is arranged to automaticaly put in a.return right of way call, the predetermined time in that apparatus beingthe time period of relay A. Hence both embodiments fulfill thiscondition.

The stepping switch, like the cam shaft of the first embodiment, willremain in either of its two rest positions 2 or 6 unless the system isset for normally arterial or reverting operation or unless a crosstraffic call is put in by a cross lane detector actuation.

Referring to Figs. 5 and 6 the following points will be noted. Thoseelements in Figs. 5 and 6 which correspond closely with specific partsshown in Figs. 3 and 4 are designated in Figs. 5 and 6 by the samenumber or letter used in Figs. 3 or 4 with the letter Z added, as forexample the signals in Fig. 3 are numbered to inclusive and in Fig. 5are designated as Z45 to Z50 inclusive.

The stepping switch contact banks, designated as SBI to $36 inclusive,are shown in Figs. 5 and 6 to the right of the grounded power wire whichextends from the bottom to the top of both figures just to the left ofthe center. The

stepping switch driving magnet, designated as DM, is shown in the lowerleft corner of Fig. 6. This magnet DM drives the wipers WI to W8 inunison over-the banks SBI to SE8 respectively. Beside it is a rectifierused to supply D. C. for the driving magnet coil.

The signals shown at the top of Fig. 5 are controlled by relays ALR andBLR. The apparatus to the left of the grounded power wire in Fig. 5 isin general effective to co-operate with the apparatus of Fig. 6 to calland hold the right of way on the NS lane whereas that to the right ofthe grounded power wire similarly cooperates with the apparatus of Fig.6 to call and hold the right of way on the EW lane.

Relay AM is energized thru contacts in step ping switch bank SB! whenthe stepping switch is in positions 2 and 3, the N-S rest position andthe N-S traflic timed positions respectively. Right of way can be calledto the N-S lane by the de-energization of relay AM which can occur inresponse to a N4 trafllc actuation when the right of way is not on theNS lane. Furthermore if the right of way leaves the NS lane thru actionof the maximum timer relay MXR or the variable vehicle interval timerrelay VVR the relay AM will be de-energized thus putting in a call forthe return of the right of way to the lane from it is being withdrawn,in this instance the N-S lane. It will be remembered that the placing ofa return call has been mentioned as a function of both the maximum timerand the variable vehicle interval timer.

If on the other hand the right of way is transferred from the N--'S laneby action of the normal vehicle interval timer relay YR, relay AM willnot be de-energized but will remain locked in thru subsequent steppingswitch positions unless it is de-energized by the actuation of a N-Svehicle detector in order to call the right of way to the N-S lane.

Relay-BM performs similarly with respect to the E-W lane, being operatedthru contacts of stepping switch bank SBI when the stepping switch is inposition 6 or I, the EW rest and traffic timed positions respectively.It is deenergized to put in an E--W return call as the right of way iswithdrawn from the E--W lane if said withdrawal is caused by the maximumtimer relay MXR or the variable vehicle interval timer relay VVR butremains locked in if said withdrawal of the right of way is caused bythe operation of the normal vehicle interval timer relay YR. Relay BM insubsequent stepping switch positions can be de-energized by action ofrelay FZ in response to an actuation of EW detector Z52 in order to callthe right of way to the E-W lane.

Relay AR which is energized by stepping switch contacts of bank SBI instepping switch positions I, 2, 3 and 4, the NS right of way and amberpositions, energizes signal relay ALR and completes certain of thetiming condenser circuits as will later be explained in detail.

Relay BR is energized in stepping switch positions 4, 5, 6 and l tosimilarly energize signal relay BLR and connect other timing condensercircuits.

The maximum timer, effective in the N% and E--W traffic timed steppingswitch positions 3 and 1 to limit the time during which moving trailiccan hold the right of way against waiting cross traffic, includes relayMXR, plate condenser KMX and tube MXT.

The variable vehicle interval timer includes relay VVR, tube VVT, platecondenser KVV and grid condensers KGNS and KGEW. It times the variablevehicle intervals in stepping switch positions 3 and I, the charge incondensers KGNS and KGEW being affected respectively by EW and N--Strafflc so as to decrease the variable vehicle interval in the N-SfandE-W lanes respectively in accordance with the amount of waiting crosstraflic as previously mentioned.

Relay YR, tube YT and condenser KV cooperate to' time the normal vehicleinterval, with the ,stepping switch in position 3 or 1, which intervalstarts simultaneously with the variable vehicle interval after eachvehicle actuation in the lane having the go signal. The timing of thenormal vehicle interval it will be remembered is not affected by waitingcross traihc whereas the timingof the variable vehicle interval isaffected stop signal in order to time the NS initial interval inaccordance with the amount of NS traflic waiting at the beginning of theNS go signal display period.

Relay YR and tube YT cooperate similarly with condenser KIEW to time theE--W initial interval, stepping switch in position 5, in accordance withthe amount of E-W trafllc waiting at the beginning of the E-W go signaldisplay period, the starting charge in condenser KIEW beingpredetermined in accordance with the amount of said waiting E-W traflic.

The same relay and tube cooperate with condenser- KY to time a minimumperiod during which the stepping switch remains in its rest positions 2and 6 in order to ensure that when the go signal is given to alane itwill remain there for a reasonable minimum period. At the expiration ofsaid minimum period the right of way will be transferred to the otherlane only' times the NS and E--W amber or warning periods, steppingswitch in position 4 f and 8 respectively.

To more completely descibe the features of the embodiment of myinvention shown in Figs. and 6 I shall now explain its operation thru acomplete signal and stepping switch cycle beginning in the NS initialinterval when the right of way has just been given to the N--S lane,stepping switch in position I. r

In this stepping switch 'position relay AR is operated, current beingsupplied thru the circuit starting at grounded power thence thruposition I of stepping switch bank SBI to relay AR to A. C. plus power.Relay AR when operated causes signal relay ALR to be energized thru thecircuit starting at A. C. plus, thru relay ALR, wire 202 to contact arlof relay AR thence to grounded power. Relay BB is de-energized instepping switch position I, its circuit being open at stepping switchbank SE2. Hence signal relay BLR is de-energized since its operatingcircuit includes contact brl of relay BR.

Wipers WI and W2 are of the bridging type so that the relays energizedthru them at their respective contact banks SBI and SB2 will not bede-energized as the stepping switch moves from one position to the next.

With relay ALR operated and relay BLR unoperated the NS go signal Z45will be illuminated thru the circuit beginning at grounded power, thrusignal Z45 thence to contact blrl of relay BLR thenceto connect alr4 ofrelay ALR and to A. C. plus power. The E-W stop signal Z50 isilluminated thru the circuit from grounded power to A. C. plus powerincluding signal Z50 and contact alr2 of relay ALR. The circuits to theother four signals are incomplete in stepping switch position I.

Explanation of the relay AM coil circuit will be helpful at this pointas an aid in following this Relay AM has an operating circuit fromgrounded power thru wiper'W2, stepping switch bank SE2 positions 2 and3, wire 206, .205, coil of relay AM, wires 204, 216, 2'", 221, contactdm2 to A. C. plus. It has in addition a holding circuit from groundedpower thru contact ezl of relay EZ, contact aml of relay AM, wire 205,coil of relay AM, wires 204, 216, 211 to contact am2 of relay AM, wire219, contact marl of maximum timer relay MXR, contact curl of variablevehicle interval timer relay VVR, thence to A. 0. Plus power.

In stepping switch position 2 relay AM is energized thru the operatingcircuit described above. That part of the operating circuit supplyingcurrent to the left side of the coil remains complete from the time thestepping, switch enters position 2 until it leaves position 3 afterwhich it is broken at bank SE2. Wiper W2 is of the bridging type toinsure continuity of the above circuit as the stepping switch moves fromposition 2 to 3.

That part of the operating circuit energizing the right side of the coilof relay AM will be opened at contact dm2 as the stepping switch movesfrom position 2 to 3. However that portion of the holding circuitparallelling the last named part of the operating circuit remains intactto supply relay AM with A. C. plus power while contact dmZ is openduring the stepping switch movement. From the above description it canbe seen that relay AM is always energized when the stepping switch is inposition 2 or 3 and when it is moving from position 2 to position 3.

The functioning of relay AM in subsequent stepping switch positions willbe explained as the circuit operation in each position is considered.

The NS initial interval is timed by relay YR, tube YT and condenserKINS. During this interval condenser KINS is connected to relay YR andto the plate of tube YT thru the circuit going from grounded power tocondenser KINS to wires 282, 290, 284 to stepping switch bank SB3position I to wiper W3, wires 224, 225 to coil of relay YR, wire 26!] toplate of tube YT. During the NS initial interval condenser KINS ischarged thru the circuit starting at grounded power, to condenser KINS,wires 282, 290, 284, to stepping switch bank SE3 position I to wiper W3,wires 224, 223 to timing resistance RZ5, wire 2, to stepping switch bankSB4 position I, to wiper W4, wire 226 to stepping switch driving magnetcontact dml to D. C. plus power. When condenser KINS is charged to apredetermined voltage the tube YT will break down, i. e., becomeconducting, thereby connecting relay YR to ground and allowing condenserKINS to discharge thru relay YR which will therefore operate and thrucontact yrl connect the rectifier associated with the driving magnet DMto power thus energizing the stepping switch driving magnet DM whichwill thereupon move the stepping switch into its next position. To varythe duration of the NS initial interval the rate at which condenser KINSis charged in stepping switch position I can be adjusted by regulatingthe variable charging resistance RZ5.

It has previously been stated that the initial interval is by theapparatus of Figs. 5 and 6 as well as by that of Figs. 3 and 4 timedsubstantially in accordance with the amount of waiting cross trafiicthru having the charge in the initial interval timing condenser at thebeginning of the initial interval predetermined by such waiting crosstrailic. In this connection consider specifically the NS initialinterval during which the stepping switch is in position I.

While the stepping switch was last in positions 2 and I relay AM wasenergized as has been previously explained. Therefore in thesetwoistepping switch positions condenser KENS was charged thru thecircuit from grounded power to condenser KINS, wires III. III, contactand of relay AM, to resistance RZIS, wire 22. to pctentiometerresistance PZ I. The maximum voltage to which condenserKINS can becharged by this circuit is predetermined by the point on thepotentiometer PZ'I to which wire 228 is attached. The rate at whichcondenser KINB is so charged can be regulated by the adjustment ofvariabl resistance RZII.

While condenser ms was being charged in.

stepping switch positions 2 and 8 as explained above andduringsucceeding intervals up .to the I EW amber period immediately precedingthe next NS initial interval, i. e., while the stepping switch was inpositions 2, I, l, 6, 6 and I, the charge of condenser KINS was subjectto the removal of an increment of charge by action of condenser KZI ateach actuation of NS detector ZSI just as, in the embodiment shown inFigs. 3 and 4 the charge in condenser KE was removed in increments byaction of condenser Kl.

The fact that increments of charge are removed from condenser ms inresponse to NS actuations even during the NS go signal display periodprovides a means whereby those NS vehicles which, under heavy tramcconditions, are stopped by loss of right of way after having actuatedthe NS detector make their presence effective to increase the next NSinitial interval.

The removal of increments of charge from condenser KINS is accomplishedthru the following circuit including contacts of relay EZ. Con denserKINS is connected to contact es! of relay EZ thru contact am3 of relayAM in stepping switch positions 2 and 3 and thru contact bi"! of relayBR in stepping switch positions 4, 6, 6 and 1. Hence in all of thesenamed stepping switch positions actuations of NS detector Z5I whichoperates relay EZ will cause contact es! and cs3 to cooperate to removean increment of charge from condenser KINS just as contacts el and c2did in the embodiment of my invention shown in Figs. 3 and 4.

The charge so removed from condenser KINS by waiting NS trafflc isreplaced thru resistance RZS during the initial interval thus timingsaid initial interval in accordance with the amount of such waiting NStrafllc. When; condenser KINS is so recharged, i. e., when the NSinitial interval is over, tube YT becomes conductive and condenser KINSdischarges thru relay YR which thereupon operates. The stepping switch,as previously explained, thereupon moves on into position 2, the NS restposition. During the movement of the stepping switch from position I to2 condenser KY is discharged thru driving magnet contact dmi inpreparation for its use as a timing condenser in stepping switchposition 2.

If the system is not set for normal reversion to the E--W lane and thereis no waiting EW traffic the stepping switch will remain in this NS restposition and the NS lane will be continuously accorded the go signaluntil an EW traihc actuation shall occur.

In stepping switch position 2, the NS go signal rest position, relay YR,tube YT and condmser KY time a ed minimum periodattheendofwhichthestepping switch can be moved on into position I eitherby an EW traiiic actuation or by normal reversion.

The circuit connectingrelayYR, tuheYTand.condmserKYinsteppingswitchpositionlisss follows. Relay YR thru wires226, I24, wiper WIandpositionlofbankBBIisconnectedto 'condmser KY thruwires 226 and 266. In addias the stepping switch moves from one positionto the next there will be no interconnection of condenser circuits.Contact dml is included in the charging circuit described above toprevent the plate or tube YT from being charged to flashover voltageduring the instant that condenser KY is disconnected therefrom as wiperW1 moves from one stepping switch position to another.

The timing of the NS minimum rest position period can be adjusted byregulating resistance RZII to control the charging rate of condenser KYin stepp n switch position 2.

The grid circuit of tubeYT in stepping switch position 2 is connectedthru wire 26!, wiper W6 and position 2 of bank 836, wire "I topotentiometer PZS. Wiper W6 is of the bridging type to preventfluctuations in grid potential as the stepping switch moves from oneposition to the next.

It will be noted that the resistance PZl and PZ6 are arranged in seriesacross the D. .C. plus and minus power terminals, and that the Junctionpoint of PZ'I and PZ6 is-connected to the central vertical ground wire,thus providing a potentiometer arrangement in which ground potential andthe left end of P26 are more positive than the right end, and variouspoints on PZI may be tapped for different negative voltages with respectto ground. PM and PZS are adapted to be individually connected betweenD. C. minus and ground, and when either is so connected it provides apotentiometer across the resistance PZ6. The negative end ofpotentiometer PZE is permanently connected to D. C. minus but thepositive end of PZS is connected to ground thru a circuit including wire254 and contact bm6 of relay BM or EW arterial switch Z66. Hence if bothswitch Z69 and contact bm6 are open the potential of the grid of tube YTwill be biased negative to such a degree that said tube .will not breakdown even though plate condenser KY be charged to its maximum positivevoltage. Therefore with contact bm6 and switch Z69 open the steppingswitch will remain at rest in position 2 even after condenser KY hasbecome fully charged.

The above condition prevails if the system is not set for normalreversion to the EW lane and there is no waiting EW traflic. Under theseconditions the stepping switch remains in position 2, its NS restposition, and the go signal continues to be displayed in said NS laneuntil the next EW traflic actuation occurs.

If normal reversion to the EW lane is desired switch Z69 is closed whichwill make the grid potential of tube YT less negative so that the tubewill breakdown" and operate relay YR causing the stepping switch to movefrom posinal and the EW stopsignal remain displayed,

detector Z52 which will de-energize relay BM by opening its holdingcircuit at contact 12! of relay F2. The de-energization of relay BMcauses contact bmG to complete a circuit connecting potentiometer PZ5 toground thus making the grid potential of tube YT much'less negative soas to cause the tube to break-down and relay YR: to operate, causingthestepping switch to move from position 2 to 3. If an actuation ofdetector Z52 takes place before the expiration of the re t positionminimum period said stepping switq movement will take place at the endof this minimum period.

In stepping switch position 3 the NS go sigand three timers, the normalvehicle interval timer, the variable vehicle interval timer and themaximum timer run concurrently. The first two of these timers aresubject to reset by N-S detector actuations and the timing period of thevariable vehicle interval timer is in addition shortened by waiting EWtraflic in accordance with the amount of such waitingEW trafiic. Themaximum timer is not affected by trailic in either lane and sets amaximum limit beyond which N-S traflic cannot continue to hold the rightof way against the cross lane.

The normal vehicle interval timer'includes relay YR, tube YT andcondenser KV. The ,grid of tube YT is in stepping switch position 3connected to potentiometer PZ6 thru position 3 of bank 835. The circuitfrom relay YR to .wiper W3 of bank SE3 has been traced. Thru this bank,in position 3, condenser KV is connected to relay YR by wires 23, 232,233 and 234.

Condenser KV, while the stepping switch was in positions I and 2, wasbeing charged thru a circuit including grounded power to condenser KV,wires 234, 233, 232 and 230 to variable resistance RZII, wire 238contact ar4 of relay AR. to positive D. C. power. In stepping switch'positions I and 2 condenser KVwas also subject to discharge by N'--Sdetector actuations thru contact e24 of relay EZ, wire 231, contact ar2of relay AR to ground. If, when the stepping switch enters position 3,the trailic in the N--S lane has'cleared the intersection condenser KVwill have had sufficient time since the last N-S detector actuation tobecome fully charged. In stepping switch position 3 condenser KV isconnected to the plate of tube YT. Hence if this condenser is fullycharged when the stepping switch moves into position 3 tube YT willimmediately breakdown and operate relay YR to move the stepping switchon into position 4 with no appreciable stop in position 3. If on theother hand N-S detector actuations have recently discharged condenser KVthe normal vehicle interval timer will continue its timing as long asthe stepping switch remains in position 3.

The variable vehicle interval timer includes relay VVR, tube VVT, platecondenser KVV and, in stepping switch position 3, gridcondenser KGNS. Instepping switch position 3 plate condenser KVV is charged thru a circuitfrom grounded power to condenser KVV, wire 263, 26!, 222, Hi, 220,variable resistance RZ4, wire 212 to position 3 of bank SB4, wiper W4,wire 226, contact dml to D. 0. plus power. Wiper W4 is or thenon-bridging type to prevent interconnection of charging circuits duringstepping switch movement. Contact dml is included in this circuit toprevent tube fiashover during the'stepping switch movement as has beenexplained before.

Condenser KVVis subjecttojdischarge upon actuation of N-S detector Z51thru the circuit from grounded powerto contact arG of "relayAR tocontact 625 of relay EZ thru' wire 240 which ties into the condenser KVVcharging circuit at wire 222 The grid of tube W1 is connected tocondenser KGNS thru the circuit including wire 249, contact br5 of relayBR and wire 245 to condenser KGNS, thence to ground. The charge ofcondenser KGNS has in previous stepping switch positions been made lessnegative by the introduction of increments of charge by .con-

denser KBNS, one increment of charge being added for each actuation ofEW detector Z52, so that the charge on condenser KGNS when the steppingswitch is in position 3 is in accordance with the amount of waiting EWtraflic.

, The circuits which accomplish the above results are as follows: Instepping switch positions 6 and I condenser KGNS is charged negativelythru the circuit from grounded power to con denser KGNS, wires 246, 241,contact bm5, variable resistor RZ20, wire 255 topotentiometer P26. Thepoint at which wire 255 makes contact with potentiometer PZS fixes themaximum negative potential to which condenser KGNS can be pmiged"by thiscircuit. The rate at which this charge takes place can be regulated byadjusting resistance RZ20.

The introduction of increments of charge into condenser KGNS isaccomplished as follows. In

all stepping switch positions condenser KBNS is charged to a.predetermined potential and then discharged into condenser KGNS once foreach actuation of EW detector Z52. This detector operates relay FZ whosecontacts fzG and f2! are effective to accomplish the above as follows.With contact is! closed condenser KBNS is charged to a predeterminedvoltage thru the circuit including grounded power, condenser KBNS, wire248, contact ,fz'7 wire 250 to potentiometer F26. The voltage to whichcondenser KBNS is so charged is regulated by setting the point at whichwire 250 contacts potentiometer PZG. A vehicle actuation of'E--Wdetector Z52 opens this charging circuit at contact I21 and connectscondenser KBNS to condenser KGNS thru the direct circuit includingcontact 126. The charge in condenser KBNS, which was regulated to beless negative than that of condenser KGNS, will therefore cause thevoltage on condenser KGNS to become less negative. Hence, when thestepping switch reaches position 3 the charge in condenser KGNS will bein accordance with the total of all the increments introduced bycondenser KBNS in response to EW trafiic actuations and will besubstantially in accordance with the number of such EW actuations sincethe right of way last left the EW lane.

The fact that increments of charge are introduced into condenser KGNS inresponse to EW traflic actuations even during the E--W go signal displayperiod provides a means whereby those EW vehicles which, under heavytraffic conditions, are stopped by loss of the right of way after havingactuated the EW detector make their presence felt in decreasing the nextN--S

